ApsaraDB RDS：ST_TrajMerge

文法

trajectory ST_TrajMerge (trajectory SET_ trajs);
trajectory ST_TrajMerge (trajectory SET trajs, bool doSort, bool doDeduplicate);
trajectory ST_TrajMerge (trajectory[] trajs, bool doSort default true, bool doDeduplicate default true);

參數

傳回值

合并後的一條軌跡。

描述

• 將多條軌跡合并為一條。

• 支援使用doSort參數將彙總的軌跡和軌跡點進行重新排序，也支援使用doDeduplicate參數將相鄰軌跡的重複軌跡點合并（例如前一條軌跡的終點是後一條軌跡的起點）。

• 建議將doSort和doDeduplicate選擇為true（預設值），雖然略微降低效能，但可以保障結果的準確。

樣本

1. 準備資料：

   CREATE TABLE test_trajs_merge(traj trajectory);
   INSERT INTO test_trajs_merge
   VALUES 
       ('{"trajectory":{"version":1,"type":"STPOINT","leafcount":2,"start_time":"2000-01-01 00:00:00","end_time":"2000-01-02 00:00:00","spatial":"LINESTRING(0 0,4 0)","timeline":["2000-01-01 00:00:00","2000-01-02 00:00:00"]}}'),
       ('{"trajectory":{"version":1,"type":"STPOINT","leafcount":2,"start_time":"2000-01-02 00:00:00","end_time":"2000-01-03 00:00:00","spatial":"LINESTRING(4 0,2 0)","timeline":["2000-01-02 00:00:00","2000-01-03 00:00:00"]}}'),
       ('{"trajectory":{"version":1,"type":"STPOINT","leafcount":2,"start_time":"2000-01-04 00:00:00","end_time":"2000-01-05 00:00:00","spatial":"LINESTRING(2 2,3 3)","timeline":["2000-01-04 00:00:00","2000-01-05 00:00:00"]}}'),
       ('{"trajectory":{"version":1,"type":"STPOINT","leafcount":2,"start_time":"2000-01-03 00:00:00","end_time":"2000-01-04 00:00:00","spatial":"LINESTRING(3 0,2 2)","timeline":["2000-01-03 00:00:00","2000-01-04 00:00:00"]}}'),
       ('TRAJECTORY EMPTY'),
       (NULL);

2. 使用情境：

   • 不排序和去除重複點：

     SELECT st_TrajMerge(traj, false, false) FROM test_trajs_merge;

     結果顯示如下，可能有多個重複點且時間亂序：

      {"trajectory":{"version":1,"type":"STPOINT","leafcount":8,"start_time":"2000-01-01 00:00:00","end_time":"2000-01-05 00:00:00","spatial":"LINESTRING(0 0,4 0,4 0,2 0,2 2,3 3,3 0,2 2)","timeline":["2000-01-01 00:00:00","2000-01-02 00:00:00","2000-01-02 00:00:00","2000-01-03 00:00:00","2000-01-04 00:00:00","2000-01-05 00:00:00","2000-01-03 00:00:00","2000-01-04 00:00:00"]}}

   • 排序但不去除重複點：

     SELECT st_TrajMerge(traj, true, false) FROM test_trajs_merge;

     結果顯示如下，時間正確但有重複點：

     {"trajectory":{"version":1,"type":"STPOINT","leafcount":8,"start_time":"2000-01-01 00:00:00","end_time":"2000-01-05 00:00:00","spatial":"LINESTRING(0 0,4 0,4 0,3 0,2 0,2 2,2 2,3 3)","timeline":["2000-01-01 00:00:00","2000-01-02 00:00:00","2000-01-02 00:00:00","2000-01-03 00:00:00","2000-01-03 00:00:00","2000-01-04 00:00:00","2000-01-04 00:00:00","2000-01-05 00:00:00"]}}

   • 去除重複點但不排序：

     SELECT st_TrajMerge(traj, false, true) FROM test_trajs_merge;

     結果顯示如下，部分時間戳記錯誤，且錯誤部分的重複點沒有被去除：

     {"trajectory":{"version":1,"type":"STPOINT","leafcount":7,"start_time":"2000-01-01 00:00:00","end_time":"2000-01-04 00:00:00","spatial":"LINESTRING(0 0,4 0,2 0,2 2,3 3,3 0,2 2)","timeline":["2000-01-01 00:00:00","2000-01-02 00:00:00","2000-01-03 00:00:00","2000-01-04 00:00:00","2000-01-05 00:00:00","2000-01-03 00:00:00","2000-01-04 00:00:00"]}}

   • 去除重複點並排序：

     SELECT st_TrajMerge(traj) FROM test_trajs_merge;

     結果顯示如下：

     {"trajectory":{"version":1,"type":"STPOINT","leafcount":6,"start_time":"2000-01-01 00:00:00","end_time":"2000-01-05 00:00:00","spatial":"LINESTRING(0 0,4 0,3 0,2 0,2 2,3 3)","timeline":["2000-01-01 00:00:00","2000-01-02 00:00:00","2000-01-03 00:00:00","2000-01-03 00:00:00","2000-01-04 00:00:00","2000-01-05 00:00:00"]}}

   • 使用軌跡數組作為參數，去除重複點並排序：

     SELECT st_TrajMerge(array_agg(traj), true, true) FROM test_trajs_merge;

     結果顯示如下：

     {"trajectory":{"version":1,"type":"STPOINT","leafcount":6,"start_time":"2000-01-01 00:00:00","end_time":"2000-01-05 00:00:00","spatial":"LINESTRING(0 0,4 0,3 0,2 0,2 2,3 3)","timeline":["2000-01-01 00:00:00","2000-01-02 00:00:00","2000-01-03 00:00:00","2000-01-03 00:00:00","2000-01-04 00:00:00","2000-01-05 00:00:00"]}}